Nowadays modern amplitudes techniques are used to compute the amplitudes in the massless double-cut.
Simplifications come from the use of generalized unitarity[1]}, a method originally developed in the context of Yang-Mills theories which outlines a systematic scheme for building loop amplitudes from simpler tree-level ones. On the same note, the double copy construction [2]} is used to establish a systematic connection between gravity and gauge theory scattering amplitudes, giving the chance to work with the latter, which are more manageable, and recover with contained effort the corresponding results for gravity.
